This invention relates to hindered amine light stabilizers in which the hindered amine is attached to the nitrogen of an imide which is attached to an aromatic group containing a carboxylic acid or derivative thereof.
Hindered amine light stabilizers (hereinafter referred to as "HALS") are a well-known class of compounds known to prevent and retard the degradation of polymers in which they are incorporated (Kirk-Othmer Encyclopedia of Chemical Technology, 3rd Ed., Vol. 23, "UV Stabilizers", pp. 615-627). Many patents on HALS additives and monomers have been issued, e.g., U.S. Pat. No. 4,336,183. The fundamental HALS functionality is a rather small molecular ensemble, generally water soluble; this prohibits use of simple, low molecular weight HALS because they are readily leached from the polymer substrate upon exposure to moisture.
HALS imides such as N-(2,2,6,6-tetramethyl-4-piperidinyl)maleimide are known and have been used to prepare HALS-containing copolymers (as in U.S. Pat. No. 4,569,997 and British Patent Application Publication No. 2,145,100 A). Other N-(2,2,6,6-tetramethyl-4-piperidinyl)imides are disclosed in U.S. Pat. No. 4,356,307, but the disclosed compounds are non-aromatic imides. N-(2,2,6,6-tetramethyl-4-piperidinyl)phthalimide and N,N'-bis-(2,2,6,6-tetramethyl-4-piperidinyl)pyromellitic diimide have been disclosed as polymer stabilizers in U.S. Pat. No. 3,904,581, although neither compound was prepared nor tested.
No reference to the instant invention could be found in the literature.